As part of various surgical procedures, an extracorporeal blood circuit is used to temporarily collect blood drained from the patient and return the blood to the patient prior to completion of the procedure. The blood reservoir may store venous blood and cardiotomy blood. For cardiovascular surgical procedures cardiopulmonary bypass systems are utilized to perform blood oxygenation and circulatory support while normal cardiopulmonary function of a patient is interrupted or impaired. A cardiopulmonary bypass system typically includes an oxygenation device for oxygenating blood before it is returned to the patient, a heat exchanger to regulate blood temperature, a pump to regulate the flow of blood, and a blood reservoir for collecting blood.
The cardiopulmonary bypass system usually collects two types of blood from the patient: venous blood, collected through the patient's vascular system, and cardiotomy blood, suctioned from the surgical site. Different tubing and filters may be used when drawing these two types of blood from the patient, but venous and cardiotomy blood are usually combined prior to reinfusion into the patient by a common line.
It is critical that air or gas bubbles entrained in the venous and cardiotomy blood are removed prior to reinfusing the blood into the patient. Air bubbles introduced into the patient's vascular system may occlude the capillaries of various organs of the patient resulting in various life-threatening conditions. The air bubbles can be of various sizes ranging from bubbles visible to an observer to tiny micro-emboli that can pass through fine mesh screens and are difficult to detect. Since there may be no filters in the bypass system between the output of the blood reservoir and the patient, it is essential that the blood reservoir remove gas bubbles, including micro-emboli. Also, it is important that the blood reservoir minimize stagnation of the blood.
Prior art blood reservoirs have assumed various shapes and incorporated various filters and vent tubes for removing air bubbles. For example, U.S. Pat. No. 4,734,269 disclosed a flexible-bag reservoir having an inlet on the bottom of the bag expelling blood into an envelope-like filter. Other examples of blood reservoirs are disclosed in U.S. Pat. Nos. 5,061,236, 4,795,457, and 4,493,705.
It is apparent that although the prior art devices provide some bubble removal, there remains a need for more effective gas bubble removal, particularly for the above-described micro-emboli. Further, there remains a need for such a blood reservoir with an improved blood flow performance to reduce blood stagnation in the reservoir.